Fuel burner

ABSTRACT

An improved fluent fuel burning apparatus including three individual airflow passages and separate means for apportioning the flow of combustion air among the passages so as to achieve complete combustion of the fuel while reducing the formation of nitric oxides.

United States Patent Peterson et al. 1 Sept. 9, 1975 FUEL BURNER3,133,731 5/1964 Reed 43l/I87 x 3,39L98l 7/l968 Voorheis ct a]. 4 i43l/l85 [75] Inventors- Petersom Medma; Bret 1700.376 10/1972 Niepenbergct a], v. 43 1/188 x C. Krlppene, Barberton; David M. Marshall, Akron.all of Ohio [73] Assignee: The Babcock & Wilcox Company, Primaryliw'1li'ler-Edward Fdmrs New Yurk NY Attorney, Agent, or Firm-Joseph M1Maguire; Robert 1. Edwards [22] Filed: May 22, 1974 [2]] Appl. No:472,583

[57] ABSTRACT [52] U.S. Cl 431/184; 239/404 [5|] Int. CL" 4 4 i 1 l 1 wv 1 1 v 1 y l F 1 An improved fluent fuel burning apparatus including[58] Fi l f 563ml] three individual airflow passages and separate means1 for apportioning the flow of combustion air among the 239/423, 404passages so as to achieve complete combustion of the fuel while reducingthe formation of nitric oxides. [56] References Cited UNITED STATESPATENTS 5 Claims, 2 Drawing Figures 2,485.656 lO/l949 Raskin 431/187 5494 4 4 I 96 9s 91 7/, O

52 6O 7lA 7o r 1 56 80 a2 1 42 8 71 7o\ 68A 1 78 2a 44 40 1'. 22:3 ill70A.) "219% J 81 as as 3 12 71A 5a 74 I 56 as m 46 7 2i 6 v 54 87 92 50T r 2 9o I 93 j if: 15 A 94 j 4 PATENTED 91975 FUEL BURNER BACKGROUND OFTHE INVENTION The present invention relates to fuel burners and moreparticularly to an improved fluent fuel burner for reducing theformation of nitric oxides by lowering the combustion zone temperatureand providing a reducing atmosphere in the ignition zone.

There is a present day growing concern with the immediate and long termproblems created by the rapid increase in air pollution resulting fromthe rise in the industrial civilization level throughout the world. Withthis concern comes an acute awareness that immediate steps must be takento reverse this upward trend in pollution and great efforts are nowbeing made by public and private economic sectors to develop measuresfor preventing potentially polluting particles and gases from beingdischarged into the atmosphere. One such source of atmospheric pollutionis the nitrogen oxides (NO present in the stack emission of fossil fuelfired steam generating units. Nitric oxide (NO) is an invisible,relatively harmless gas. However, as it passes through the vaporgenerator and comes into contact with oxygen, it reacts to form nitrogendioxide (N or other oxides of nitrogen collectively referred to asnitric oxides. Nitrogen dioxide is a yellow-brown gas which, insufficient concentrations is toxic to animal and plant life. It is thisgas which may create the visible haze at the stack discharge of a vaporgenerator.

Nitric oxide is formed as a result of the reaction of nitrogen andoxygen and may be thermal nitric oxide and/or fuel nitric oxide. Theformer occurs from the reaction of the nitrogen and oxygen contained inthe air supplied for the combustion of fossil fuel whereas the latterresults from the reaction of the nitrogen contained in the fuel with theoxygen in the combustion air.

The rate at which thermal nitric oxide is formed is dependent upon anyor a combination of the following variables; l flame temperature, (2)residence time of the combustion gases in the high temperature zone and(3) excess oxygen supply. The rate of formation of nitric oxideincreases as flame temperature increases. However. the reaction takestime and a mixture of nitrogen and oxygen at a given temperature for avery short time may produce less nitric oxide than the same mixture at alower temperature, but for a longer period of time. In vapor generatorsof the type hereunder discussion wherein the combustion of fuel and airmay generate flame temperatures in the order of 3,700F, thetime-temperature relationship governing the reaction is such that atflame temperatures below 2,900F no appreciable nitric oxide (NO) isproduced, whereas above 2.900F the rate of reaction increases rapidly.

The rate at which fuel nitric oxide is formed is principally depcndenton the oxygen supply in the ignition zone and no appreciable nitricoxide is produced under a reducing atmosphere; that is, a conditionwhere the level of oxygen in the ignition zone is below that requiredfor a complete burning of the fuel.

It is apparent from the foregoing discussion that the formation ofthermal nitric oxide can be reduced by reducing flame temperatures inany degree and will be minimized with a flame temperature at or below2,90()F and that the formation of fuel nitric oxide will be inhibited byproviding a reducing atmosphere in the ignition zone.

With the advent of stricter emission controls, manufacturers of fuelburning equipment have been actively seeking methods of limiting theamount of pollutants which are formed from the combustion of fossilfuel.

U.S. Pat. No. 3,788,796 issued to Krippene et al. and assigned to theAssignee of the present invention discloses a technique used withrelation to burning pulverized fuel and which achieves a reduction inthe formation of nitric oxide and results in a more complete burning ofthe fuel.

SUMMARY OF THE INVENTION The present invention provides an apparatus forreducing the formation of nitric oxide while achieving a more completeburning of fluent fuel than has heretofore been possible.

Accordingly, an apparatus is provided for the burning of fluent fuelswherein at least a part of the apparatus is disposed within a windbox towhich combustion air is supplied and which is formed between adjacentburner and furnace walls of a vapor generating unit. The burner wall isformed with an access opening for admitting that portion of theapparatus which normally resides in the windbox whereas the furnace wallis formed with a burner port which accommodates the combining of fueland air into a combustible mixture and the ignition thereof. Theapparatus includes an open ended member disposed within the windbox andforming a central passageway of circular cross-section coaxiallyarranged with and having its discharge end opening to the burner port. Aconduit having a portion thereof concentrically spaced about the openended member forms therebetween a first annular passageway discharginginto the burner port. A register concentrically spaced about a portionof the conduit defines therewith a second annular passageway discharginginto the burner port. Means are provided within the windbox to apportionthe combustion air between the aforementioned passageways. Nozzle meansextend through the windbox to introduce a fluent fuel into the burnerport in a pattern substantially symmetrical with the axis of the port.

An object of the invention is to provide a fluent fuel burning apparatuswherein initial burning is conducted in a fuel rich climate to cause areducing zone which inhibits the formation of fuel nitric oxide andprovides the lower peak flame temperatures required to minimize theformation of thermal nitric oxide.

Another object of the invention is to limit the initial mixing of thefluent fuel and air to cause a recirculating zone which creates a flamestabilizing effect.

A further object of the invention is to admit the remaining air requiredfor complete combustion along a flow pattern which surrounds thereducing and stabilizing zones and eventually mixes with the fluent fuelto complete its combustion.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a segmental side viewincorporating fluent fuel burning apparatus embodying the invention.

FIG. 2 is an end view of a segment of the apparatus depicted in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION The embodimentillustrated in the drawings and hereinafter described is related to afuel burning apparatus associated with a liquid fuel burner. it will beunderstood, however, that the invention is equally applicable for usewith a gaseous fuel burner.

Referring to FIG. 1, reference numeral identifies a fuel burningapparatus which is arranged to tire through a circular burner port 12,the latter being lined by refractory and formed as a frusto-conicalthroat diverging toward the furnace side of the front wall 14 and beingfluid cooled by the tubes 16. A burner or outer wall 18 is spaced fromthe furnace front wall 14 to form a windbox 20 therebetween. The burnerwall 18 includes an access opening 22 which admits that portion of thefuel burning apparatus normally residing within the windbox 20.

in the illustrated embodiment there is shown a liquid fuel burner 24 ofthe type disclosed in US. Pat. No. 2,414.459 issued to J. Fletcher andassigned to the Assignees of the present invention, and including aguide tube 26 extending through the windbox 20 in coaxial relation withthe burner port 12. The guide tube 26 has its inlet end threadablyengaged to a yoke assembly 28, the latter being connected to liquid fueland atomizing fluid supply lines (not shown). The discharge end of yoke28 is connected to a transition member 30 for the through flow of fueland atomizing fluid. A leakproof fit between the yoke 28 and the member30 is achieved by introducing a gasket (not shown) between the matingsurfaces and applying pressure with a locking device 32. A fuel tube ornozzle 34 extends through the guide tube 26 and out of the distal endthereof. The nozzle 34 is connected at its inlet end to the transitionmember 30 and is provided at its outlet end with an atomizing assemblyincluding a sprayer plate 36 which introduces the atomized fuel into theburner port 12 in a pattern substantially symmetrical with the axis ofthe port. The distal end of the guide tube 26 includes a support ring 38and an air deflecting device 40 attached thereto. The deflector 40 is inthe form of a truncated cone and is concentrically disposed about thecentral axis of the burner throat l2 and includes an opening toaccommodate the passage therethrough of the sprayer plate 36.

in accordance with the invention there is provided an open ended member42 disposed in spaced surrounding relation with a portion of the liquidfuel burner guide tube 26 and forming a central passageway 44 ofcircular cross-section coaxially arranged with and having its dischargeend opening to the burner port 12. A conduit 46 extends through thewindbox 20 and has an outlet end portion thereof concentrically spacedabout the open ended member 42 to form therebetween a first annularpassageway 48 discharging into the burner port 12. The conduit 46 hasits inlet end projecting through the closure member 50 which covers theburner access opening 18; the inlet end is in turn covered by a circularplate member 52. The burner wall 18, the closure and plate members 50and 52 are covered with insulating material 54 so as to inhibitconductive heat loss there-across. Combustion air is admitted to theconduit 46 through one or more circumferentially spaced slots 56preferably located in near proximity to the burner wall 18. The slots 56are preferably of arcuate rectangular configuration and are separated byribs 58 formed by the conduit wall. A sleeve like member 60 is locatedwithin the conduit 46 and is equipped with wheels 62 partially recessedin the sleeve wall and contacting the ribs 58 thus facilitating themovement of the sleeve member 60 across the slots 56 so as to cover apart or all of the area of the slots 56 thereby providing the means forregulating the quantity of combustion air admitted to the conduit 46.The sleeve member 60 has an external diameter slightly smaller than theinternal diameter of the conduit 46 and an axial length slightly greaterthan the axial length of the slots 56. A pair of positioning rods 64,horizontally spaced from one another, have their respective distal endweldably connected to the sleeve member 60 and the opposite endterminating outside of the windbox 20 and are fitted with handleportions 66 to allow adjustment of the position of the sleeve 60 fromwithout the windbox The po sitioning rods 64 are supportingly guided bya respective tube member 68, the latter extends through the plate 52 andits insulation cover and is provided with a locking device 70 to fixedlyhold the positioning rod 64 so as to maintain the selected position ofsleeve 60 with respect to the slots 56. The distance between thetrailing edge of the slots 56 and the windbox end of the tube members 68is substantially equal to the axial length of the sleeve member so thatthe slots 58 will be fully exposed when the sleeve 60 abuts on thewindbox end of the tubes 68 thereby allowing maximum flow of combustionair into conduit 46. Stops 71 in the form of collars are provided on thepositioning rods 64 and are fixedly located so as to abut the outsideend face of the tube members 68 when the sleeve member 60 com pletelycovers the slots 56, shutting off substantially all of the combustionair flow into the conduit 46.

A plurality of vanes 72 are arranged in surrounding relationship to theopen ended member 42 and are located within the first annular passageway48, the vanes 72 are equidistantly spaced and preferably linked to oneanother so as to be collectively and simultaneously adjustable through ashaft member 74 operatively connected thereto and terminating outside ofthe windbox 20 and connected to a manually operated handle 76. The vanes72 have the principal function of imparting a rotational component tothe combustion air flowing through the first annular passageway 48.

A tubular member 78 has one end thereof rigidly connected to the plate52 and extends through the conduit 46 in spaced coaxial relationtherewith and in spaced surrounding relation with the burner nozzleguide tube 26 and axially spaced from the inlet end of the open endedmember 42. A plurality of circumferentially spaced struts 80 are locatedmidway along the axial length of the tubular member 78 and provide support for the conduit 46 through the member 78, the latter is also usedto support the guide tube 26 through a plurality of struts 81 which arecollared around the guide tube 26 and abut against the inside wall ofthe tubular member 78.

A sleeve like member 82 is slidably fitted over the forward end portionof member 78 and is movable to change the spacing 83 between its forwardend flange 85 and the inlet end face 87 of the member 42 so as toprovide the means for regulating the quantity of combustion air flowingthrough the central passageway 44. The sleeve member 82 is shown in itsfully retracted position and the spacing 83 is wide open therebyallowing a maximum quantity of combustion air to pass from the conduit46 to the central passageway 44.

A pair of positioning rods 64A, vertically spaced from one another, havetheir respective distal end weldably connected to the rear end portionof the sleeve member 82 and their opposite end terminating outside ofthe windbox and are fitted with handle portions 66A to allow positioningof the sleeve member 82 from without the windbox. The positioning rods64A are supportingly guided by a respective tube member 68A, the latterextends through the plate 52 and its insulation cover and is providedwith a locking device 70A to fixedly holdthe positioning rod 64A so asto maintain the selected position of sleeve member 82 with respect tothe open ended member 42. The struts 80 have the added function ofserving as a backstop for the sleeve member 82 so that the spacing 83 isat its maximum dimension when the rear end face of sleeve member 82abuts against the struts 80. Stops 71A in the form of collars areprovided on the positioning rods 64A and are fixedly located so as toabut the outside end of the tube member 68A when the forward end flange85 rests against the inlet end 86 of the open ended member 42 therebyclosing the spacing 83 and shutting off substantially all of thecombustion air flow into the open ended member 42.

A register assembly 87 is spaced about the conduit 46 and has one endrigidly connected to the plate 52 and the opposite end opening into theburner port 12. The register assembly 87 includes-a cylindrical housing88 d sposed in adjacent surrounding relation to the con duit 46 andincluding a portion thereof fitted with slots 89 having substantiallythe same configuration as the slots 56 and being located in superposedfashion thereto so as to provide an unimpeded flow path into the conduit46. The distal end of the housing 88 is rigidly connected to the innerperiphery of an annular plate member 90 which forms one of the wallsdefining the inlet to the register assembly 87, the other wall beingformed by an annular plate member 91 fitted with a convergingfrusto-conical section 92. The plate 91 and the section 92 cooperatewith the conduit 46 to form an annular passageway 98 therebetween.

The members 93 supportingly connect the plate 91 and the section 92 tothe front wall 14. A plurality of dampers or register doors 94 arecircumferentially spaced and pivotally mounted between the walls 90 and91 and are adapted to pivot between open and closed positions therebyproviding the means for regulating the quantity of combustion air beingadmitted to the annular passageway 98. The positioning of the dampers 94is simultaneously effected through a shaft 95 suitably linked theretoand terminating outside of the windbox 20 and fitted with an operatinghandle 96. An ignitor assembly 97 of known type extends through theclosure member 50 and the plate member 90 and terminates in the annularpassageway 98.

If desired, the positioning rods 64 and 64A and the dampers 94 may besuitably geared, linked or otherwise connected so as to be responsive toautomatically controlled actuating devices.

FIG. 2 of the illustrated embodiment is an end view of the plate member52 and the elements situated thereabout such as the handles 66 and 66Aand the locking devices 70 and 70A associated with the posi' tioningrods used to position the sleeve members which are a feature of theinvention. There are also shown a pair of observation doors 99straddling the liquid fuel burner 24 and the handle 76 associated withthe shaft used to regulate the vanes located in the central passageway.

In the operation of the preferred embodiment, liquid fuel is supplied toand atomized within the fuel burner 24 and sprayed into the port 12 in apattern substantially symmetrical with the axis of the port. The totalair required for combustion of the fuel is supplied from the windbox 20and is distributed among three separate passageways for discharge intothe port 12. The aforementioned passageways being defined as the centralpassageway 44, the first annular passageway 48 and the second annularpassageway 98. The quantity of combustion air admitted to eachpassageway is controlled by separate flow regulating means, i.e., thesleeve member 82 which is adjustable to vary the spacing 83 providingaccess to the inlet of the central passageway 44; the sleeve memberwhich is adjustable to vary the opening of the slots 56 providing accessto the first annular passageway by way of conduit 46; and the dampers 94which are simultaneously adjustable to vary the inlet opening to theregister assembly 87 including the second annular passageway 98 formedthereby. In accordance with the invention, the apparatus hereindisclosed provides the means whereby initial burning of the fuel isconducted in a reducing Zone by adjusting the sleeve member 82 so as tolimit the quantity of combustion air being discharged through thecentral passageway 44. Means are also provided whereby a flamestabilizing zone is created by adjusting the sleeve member 60 toregulate the quantity of air being admitted to the conduit 46 anddischarged through the first annular passageway 48 so as to causerecirculation of air about the outer periphery of the reducing zone.Finally, means are provided whereby the remaining air required for thecomplete combustion of fuel is regulated by adjusting the dampers 94 andis discharged through the second annular passageway 98 so as to envelopthe reducing and stabilizing zones and eventually mix with the fuel tocomplete its combustion.

Under actual operation, it has been found that maintaining thecombustion air which flows through the central passageway 44 within arange of IS to 30 percent of stoichiometric air and that which flowsthrough the first annular passageway 48 within a range of 5 to 35percent of stoichiometric air creates a stable ingition zone under areducing atmosphere and provides lower peak flame temperatures. Thecombustion air which flows through the second annular passageway 98 ismaintained within a range of S0 to percent of stoichiometric air andrepresents the air needed to complete the combustion of the fuel.

While in accordance with provisions of the statutes there is illustratedand described herein a specific embodiment of the invention, thoseskilled in the art will understand that changes may be made in the formof the invention covered by the claims, and that certain features of theinvention may sometimes be used to advantage without a corresponding useof the other fea tures.

The embodiments ofthe invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In combination with a boundary wall of a furnace, at least one burnerport formed in the boundary wall, a burner wall spaced from the boundarywall to form a windbox therebetween to which combustion air is supplied,an open ended member disposed within the windbox and forming a centralpassageway of circular cross-section coaxially arranged with and havingits discharge end opening to said port, conduit means concentricallyspaced about said Open ended member to form therebetween a first annularpassageway discharging into said port. adjustable vane means disposedwithin said first passageway, a register concentrically spaced aboutsaid conduit means to define therewith a second annular passagewaydischarging into said port, means disposed within said windbox forapportioning the combustion air between said passageways, and nozzlemeans for introducing a fluent fuel into the port in a patternsubstantially symmetrical with the axis of said port.

2. The combination according to claim 1 wherein the means forapportioning the combustion air include havtween it and said inlet end.

1. In combination with a boundary wall of a furnace, at least one burnerport formed in the boundary wall, a burner wall spaced from the boundarywall to form a windbox therebetween to which combustion air is supplied,an open ended member disposed within the windbox and forming a centralpassageway of circular crosssection coaxially arranged with and havingits discharge end opening to said port, conduit means concentricallyspaced about said open ended member to form therebetween a first annularpassageway discharging into said port, adjustable vane means disposedwithin said first passageway, a register concentrically spaced aboutsaid conduit means to define therewith a second annular passagewaydischarging into said port, means disposed within said windbox forapportioning the combustion air between said passageways, and nozzlemeans for introducing a fluent fuel into the port in a patternsubstantially symmetrical with the axis of said port.
 2. The combinationaccording to claim 1 wherein the means for apportioning the combustionair include having the conduit means formed with a slotted portion andproviding sleeve means movable across said slotted portions.
 3. Thecombination according to claim 2 wherein said sleeve means is disposedwithin the conduit means.
 4. The combination according to claim 2including rotatable means fitted in said sleeve means wall.
 5. Thecombination according to claim 1 wherein the means for apportioning thecombustion air include a member coaxially arranged with and facing theinlet end of the central passageway, said last named member beingmovable along its axis to vary the distance between it and said inletend.